POS0979 IMPROVING THE VALIDITY OF DIAGNOSTIC CODES AND POINT PREVALENCE ESTIMATION OF SPONDYLOARTHRITIS IN A LARGE POPULATION-BASED DATABASE
Authors: J. Feld, W. Saliba, N. Stein, T. Gazitt, D. Zisman
Journal: Annals of the Rheumatic Diseases (2022)

Background Large population-based databases provide an opportunity to study the epidemiology of spondyloarthritis (SpA), however, strict validation procedures for case ascertainment are required (1). Objectives To examine the validity of the ICD-9 codes of SpA in a large population-based database and to assess whether applying a specific algorithm would improve the case ascertainment. Finally, the point prevalence of SpA in the database was estimated using the validated algorithm. Methods A Database of a large public health fund, which serves approximately 3.17 million enrollees older than 18 years old, was used. The database includes real-time input from pharmaceutical, medical and administrative operating systems. At first, the database was searched for all individuals who received an ICD-9 code of SpA, 720.0: 7200, 7201, 7202, 7208, 72081 and 72089. All medical records of a random sample of 169 patients were thoroughly reviewed by a rheumatologist. Based on the information available in the database, a decision was made whether SpA diagnosis was: 1) definite/probable SpA; 2) not SpA/; not enough data to verify the diagnosis of SpA. The positive predicted value (PPV) and 95% confidence interval (CI) were calculated. In order to improve the case ascertainment, a second validation process was performed using a specific algorithm. The algorithm applied was: a permanent ICD-9 code of SpA assigned by the family physician plus at least one of the following criteria: 1. At least one visit at a rheumatology clinic either in the community or at a hospital outpatient clinic; 2. A diagnosis of SpA given during a hospital admission; 3. A prescription fulfilled of an anti-Tumor Necrosis Factor agent or anti IL-17 agent. This algorithm was validated by two rheumatologists in a random sample of 182 cases. Finally, the point prevalence of SpA was estimated applying the validated algorithm. Results The PPV of the ICD-9 codes of SpA was 44% (95%CI 36%-52%). The specific algorithm improved the PPV to 90% (95%CI 85%-94%). The concordance between the two rheumatologists was 91.3 95%CI (85.7-94.8). On the 31/12/2021, the validated algorithm identified 2892 live SpA patients older than 18 among a population of 3,167,329 enrollees in the database, reflecting a point prevalence of 0.09%, 94 patients per 100,000. Fifty one percent of the patients were male, 49% females. The point prevalence of males was 0.096%, and females - 0.087%. On the 31/12/2021, 6% of the patients were 18-29 years old, 34% 30-44 years old and 60% older than 45. Conclusion A specific algorithm can accurately identify patients with SpA in this large population-based database. The estimated prevalence of SpA is 0.09%. This figure is consistent with other population-based estimates (2). References [1]Wang R, Ward MM. Epidemiology of axial spondyloarthritis: an update. Curr Opin Rheumatol. 2018;30(2):137-43. [2]Stolwijk C, van Onna M, Boonen A, van Tubergen A. Global Prevalence of Spondyloarthritis: A Systematic Review and Meta-Regression Analysis. Arthritis Care Res (Hoboken). 2016;68(9):1320-31. Disclosure of Interests None declared